Intermittent thermal switch



@ct. 193 2- H. F. LGWENSTEIN 1,834,775

INTERMITTENT THERMAL SWITCH Original Filed April 14. 1920 cal circuits such Patented Oct. 25, 1932 UNITED STATES PATENT @FF'ECE INTERMITTENT THERMAL SWITCH Original application filed April 14, 1920, Serial No. 373,768, new Patent No. 1,684,709, issued September 18, 1928. Divided and this application filed. July 6, 1928.

The present invention relates to intermittent thermal switches and more particularly to the type known as thermal flashers for intermittently switching on and off electrielectric light circuits for advertising display, and is a division of my copending application, Serial No. 373,768, filed April 14, 1920, on which Patent No. 1,684,709 was granted September 18, 1928.

The general object of the invention is to provide a switch of the above type for either single or double circuits which will be reliable in operation, unaffected by external temperature changes and capable of rapid operatic-11 at a comparatively low operating temperature.

Another object of the invention is to provide a thermal switch capable of operating with substantially the same period for both connection and disconnection of a circuit whether working at low or high temperature or fast or slow.

Another object of the invention is to provide a device of the present type in which the amount of work required to effect a given amount of movement of the movable parts is reduced to a minimum.

Another object is to provide a novel form of heating element and means for mounting the same in operative relation to the thermomotor elementsuch that the heat insulating effect of the heating element itself is reduced to a minimum, and the space occupied by the heating element is substantially reduced.

Various other objects of the invention will be apparent from a perusal of the following specification and drawing accompanying the same.

Applicant is aware of the following patents in the art to which the present invention pertains':

United States Patents; No. 451,520 granted May 5, 1891 to E. WV. Rice J12; No. 908,679 granted Jan. 5, 1909 to W. V. DfiKelly; No. 921,625 granted May 11, 1909 to 7. J Phelps; No. 1,030,207 granted June 18, 1912 to Rawlings and Sweetser; No. 1,150,001 granted August 10, 1915 to A. H. Miller; and No. 1,150,706 granted August 17, 1915 to M.

Serial No. 290,733.

C. Ryan. Also British patent to Seabrook No. 21,131 of 1901, and British patent to Kelly No. 8,231 of 1907.

My invention is illustrated in the accompanying drawing in which Fig. l is a top plan view of a preferred embodiment of the invention, the heating elements or coils bein shown diagrammaticallyj Fig. 2 is a side eievz tion of the same with portions omitted for the sake of clearness.

Fig. 3 shows a metal blank for a modified form of the thermo-n'iotor elem Ilb of Fig. 1.

Fig. dis a further modification of the form shown in Fig. 1.

F 1g. 5 is a fragmentary detail view of a portion of the device illustrated in Fig. 4.

Referring to the drawing in detail and first to 1 and 2, the thermo-motor element is of the arched or bowed type which by the novel construction shown is rendered self compensating for external temperature changes. This is accomplished by mounting the bowed expansion bar 1 on a second expai1- sion bar 2 forming a chord, the chord being of the same material or having substantially the same coefiicient of expansion as the how. The preferred material is brass because of its high coefficientof expansion although other metals such as copper or iron maybe used. The bowed member 1 is attached atits ends to the ends of the chord member 2 by means of the upstanding ears 3 at the ends of the chord member, the parts being firmly held in any suitable manner as by the rivets shown.

By arranging the chord member with the 8 plane of its width parallel to the direction of movement of the bow member it is strengthened against bending under the forces applied thereto in operation. To hold the chord member flat during operation it is fastened at its center by a bolt i to a base 5 of suitable insulating material such as porcelain. The ends of th chord member are thus free to expand and shrink away from and toward the center, in which movement the ends are held down on the base by the heads of the bolts 6 whose shanks pass througl'ilongitudinal slots 7 inthe chord member. The chord member is spaced slightly above the base by the elevated portions 8 through which the bolts 6 pass, the

purpose of the spacing being to accommodate a suitable electrical heating element 9. A suitable heating element 10 is also provided for the bowed member 1. These heating ele ments are shown only diagrammatically in Fig. 1 for. the sake of clearness, it being understood that they may be in the form of coils of resistance wire wound on strips of mica or other insulating material and. faced or covered on each side with other strips of insulating material, which form of heating element has been described in my copending application Serial No. 373,768, filed April 14, 1920, and issued September 18, 1928 as Patent No. 1,684,709.

Both the bow and chord members are pro vided with radiating flanges which for simplicity are shown as consisting of projecting lugs or studs 11 of heat conducting material, but which may be of any number and of any form such for example as that shown in Fig. 4. To reduce the amount of force required to bend the bow member at the line of junction with its support, it is thinned out at these places as indicated at 12 to make it more flexible. It will be obvious that in lieu of this thinning out of the metal I may use extra pieces of flexible material to form the joint, with the advantage that such material may be selected for flexibility without regard to its coefiicient of thermal expansion. Mount ing posts 13 are formed on the base 5 on which are mounted the adjustable contacts 14 and 15. The bow member 1 carries a two way snap movement contact member 16 positioned between the adjustable contacts, the adjus able contact 15 passing through anopening in the bow. member into operative relation with the contact 16.

In Fig. 3 is shown a blank formed of a single piece of metal from which the thermomotor element of Fig. 1 may be formed by bending the upper portion at right angles to the lower portion along the dotted lines 17 and bowing or curving the upper portion between the dotted lines 18 with a suitable die or by hammering or other known method.

The left hand terminals of the heating elements 9 and 10 are connected to the binding posts 19 and 20 which are electrically connected with the adjustable contacts 15 and 14 respectively. The right hand terminals of the heating elements are connected in multiple to the binding post 21. The contact member 16 is electrically connected with the binding post 22 through the metal body of the bow element 1.

The outside circuit connections'for a double circuit control such as the two lamps 23 and 24, consist of the conductors 25 and 26 connecting one terminal of each of the lamps 23 and 24 with the binding posts '19 and 20, respectively, a conductor 27 connecting binding post 22 with one of the power mains 28, conductors 29 and 30 connecting the binding post 21 and the other terminals of the lamps in multiple to the other power main 31, and conductors 32 and 33 connecting the left hand terminals of the heating coils 9'and 10 with the binding posts 19 and 20 respectively.

The operation is as follows: Assuming the parts to be in the position shown, the heating element 10 will be energized and the lamp 24 lighted by current from main 28, over conductor 27, through binding post 22, how member 1, contact member 16, stationary contact 14 to binding post 20 where the circuit branches, one branch passing by way of conductor 33 through the heating coil 10, connection 21, 29 to main 31, the other branch passing over conductor 26 through lamp 24, conductor- 30 (common to both lamps) to main 31. Heating element 10 becoming energized raises the temperature of the bow member 1 which moves upwardly causing the contact member 16 to bear against the fixed contact.14 until the contact 16 is buckled downwardly just past its straight or deadcenter position when it snaps down into engagement with the fixed contact 15 and out of engagement with contact 14. This opens the circuits of the lamp 24 and heating element 10, and closes the circuits of the lamp 23 and heating element 9. The lamp 24 now becomes extinguished and the bow element 1 is permitted to cool and so move downwardly. The circuit connection now completed for the lamp 23 and heating element 9 may be traced as follows: Main 28, binding post 22, 1, 16, 15 to 19, where the circuit branches, one branchpassing by way of- 32, 9,21, 29 to main 31 and the other branch passing by way of 25, 23, 30 to main 31. Heating element 9 becoming energized, raises the temperature of the chord member 2 which expanding accelerates the downward movement of the bow member 1. The bow member moving downwardly causes the contact member 16 to bear against the contact 15 maintaining the closure of the circuits last traced until the contact member is buckled upwardly past its straight or dead-center position whereupon it snaps up into engagement with the adjustable contact 14. This opens the circuits of lamp 23 and heating element 9 and again closesthe circuits of lamp 24 and heating element 10, completing a cycle of operation which is then repeated indefinitely.

The reliability and sturdiness of the expansible bow type of thermo-motorelement is evidenced by its presence in some of the thermal flashers at present on the market and in use. However those in present use consist simply of an expansible bow element with fixed end abutments for the bow element and so are not self compensating for external temperature changes, whereas in applicants device the expansible chord member renders the thermo motor element self compensat- (Ill ing. It will be obvious that the device of Fig. 1 may be used with one heating coil either on the bow member or the chord member with the advantage 'over the present art of being self compensating. The advantages of using the two heating elements are that the thermo-motor element is not dependent whol- 1y upon the rateof cooling for the rate of retractile movement, but has its retractile movement accelerated by the expansion of the chord memberduring the cooling and shrinking of the bow member, and'does not have to operate at a high temperature in order to increase the rate of radiation to make the rate of cooling equal to that of heating. The advantage of using the radiating flanges is that the rate of cooling is increased and the rate of heating decreased thus compensating for the natural tendency to take longer to cool than to heat. The advantage of minimizing the amount of force or work expended in operation by the use of the flexible joints, is that the required thickness of the expansion elements is reduced to only that necessary to operate the contact member without distortion of the expansion elements, thus reducing the amount of heat energy required for operation. The above enumerated advantages combined, result in increased speed of operation and increased amplitude of movement over similar known devices, for a given mean Working temperature or a lower mean Working temperature for a given speed and amplitude.

It is to be understood that the curvature of the are or bow member in Fig. 1 is exaggerated for the sake of illustration, but that in practice it can be made very slight with a consequent multiplication of the amount of movement of the movable contact member. This is possible only when the flexible joints are used, for reasons which will be obvious.

The device shown in Fig. 4 is in the nature of a modification of that of Fig. 1, differing therefrom in that the bow member 34 is in the form of a toggle-lever composed of the members 35 and 36 with knife-edge bearings 37, 38 and 39 maintained seated by the retractile spring 40. The bearing 37 is formed as shown in Fig. 5 with horns 41 at the ends of the knife-edge member arranged to overlap the ends of the socket member to prevent the knife edge from sliding out of the socket. The chord member 42 is made of the same material, or a material having substantially the same coefficient of expansion, as the toggle-lever member and is similar in shape to the chord member 2 of Fig. 1 except that the abutments 43 are provided with troughs or V-sockets forming one member of the knife-edge bearings 38 and 39. A mounting post 44 is formed on the side of the chord member 42 to which the retractile spring is anchored by means of the adjust ing screw 45 which threads into the convolutions of one end of the spring, the other end of the spring being attached to the member 36 of the toggle. The chord member 42 is mounted on the base 46 in identically the same manner as that of Fig. l. A quick make-and-break two way contact member 47 iscarried by the member 36 of the toggle and plays between the two adjustable contacts 48 and 49 which are mounted on the base 46 and electrically connected with the binding posts 50 and 51 in a manner similar to that of Fig. 1 and which will be obvious to those skilled in the art from an inspection of Fig. 4. A suitable heating element 52 is provided for the chord member 42, mounted beneath the same in the same manner as that of Fig. 1. The toggle 34 is provided with a pair of heating elements 53, one for each of the members 35 and 36, connected across the middle joint of the toggle by a flexible conductor 54. One terminal of each of the heating elements is connected to the binding post 55 while the other terminals are connected individually through the flexible conductors 56 and 57 with the contacts 43 and 49, respectively, as shown. To increase the rate of cooling, all the expansion members 35, 36 and 42 are provided with radiating flanges 58.

For controlling a pair of circuits such as the circuits ofthe lamps 59 and 60, the circuit connections areas indicated in the drawing and will be clearly understood from the fol lowing description of operation.

In operation, starting with the various parts in the position shown and with current supplied over the mains 61 and 62 from a suitable source not shown, the heating elements 53 and the lamp 59 will be energized by current over the following path; main 61, body of toggle member 36, contact 47 to con tact 48, where the circuit divides, one branch passing over conductor 56, through heating elements 53, binding post 55, to main 62, the other branch passing through binding post 50, conductor 63, lamp 59 to main 62. The lamp 59 is thus lighted while the heating element 53 heats up'the toggle-lever bow member 34 which expanding buckles toward the contact 48 causing the contact member 47 to bear there-against and maintain the continuity of the circuit just described, until contact 47 is buckled past its dead-center position whereupon it snaps over into engagement with the contact 49 and out of engagement with contact 48 which opens the circuit just traced, extinguishing the lamp 59, deenergizing the heating element 53, and completing the circuits of the heating element 52 and lamp 60. The heating element 52 and lamp are now energized by current over the following path; main 61, body of toggle member 36, contact 47, contact 49, where the circuit divides, one branch passing through conductor 57, heating element 52, binding post 55 to main 62, the other branch passing through binding post 51, conductor 64, lamp to main 62. Energization of the heating element 52 causes the chord member 42 to heat up, and expanding, separate the abutments 43 which permits the toggle or bow member 34 to straighten and move toward the right by force of the spring 40, the rate of which movement being augmented by the shrinkage of the toggle or bow member due to cooling. As the bow member moves toward the right, the contact member 47 bears against contact 49 maintaining the continuity of the circuit just traced until the contact member 47 is buckled past its dead-center position whereupon it snaps over into engagement with contact 48 and'out of engagement with contact 49, opening the circuits last traced and again closing the circuits of the lamps 59 and heating elements 53. This completes one cycle of the operation which is repeated indefinitely as long as the current supply is maintained.

It is to be noted that the operation may start from a point in the cycle other than that above'described. For example, it may start with the movable contact 47 in engagement with the contact 49, in which case the first movement would be a movement of the toggle or bow member 34 to the right caused by expansion of the chord member 42. In either case, after the first cycle of operation, the movement of the bow-member to the right is accelerated by the combined eflects of its cooling and the heating of the chord memher, while movement to the left is accelerated by the combined effects of the heating of the bow member and the cooling of the chord member. By anchoring the retractile spring 40 to a post 44 carried by the chord member 42, the process of assembling is simplified, but if desirable the post 44 may be made separate from the chord member in any suitable manner to constitute a stationary support for the spring as would suggest itself to those skilled in the art.

l/Vhile I have herein shown and described certain specific embodiments of my invention for the purpose of disclosure, it is to be understood thatI do not limit myself to such specific embodiments, but contemplate all such variants and modifications thereof as fairly fall within the scope of the appended claims.

Having thus described my invention what I claim and desire to secure by Letters Patent is 1. An intermittent thermal switch having a thermo-motor element comprising a bowshaped expansible member mounted upon a compensating expansible base member, and heating and cooling means for one of said expansible members. I

2. A thermo-motor element for intermittent thermal switches comprising a bowed member in the form of a toggle lever of thermo-expansive material, and a base member of like material connecting the extreme pivots of the toggle lever and having substantially the same time constant as said bowed member in its response to external temperature changes.

3. In a thermal. switch having a bowshaped expansion element, an external temperature compensating element and a double the thernio-motor element comprises a bowed expansible member mounted upon an expansible base member having substantially the same time constant as said first mentioned expansible member in its response to external temperature changes. 1

In testimony whereof I afliX my signature.

HARRY r. LowENsTEIN. 

